1. Field of the Invention
Aspects of the present invention relate to a belt driving device, a transfer unit using the same and an image forming apparatus using the transfer unit, and more particularly, to a belt driving device having a structure capable of automatically applying tension to a belt in a loosened state when the belt begins to move, a transfer unit using the belt driving device and an image forming apparatus using the transfer unit.
2. Description of the Related Art
Generally, a belt driving device drives at least one of a plurality of rollers which are disposed at an inner circumference of a belt, thus driving the belt to rotate by friction generated between the belt and the at least one roller. The belt driving device is extensively used in various types of electrophotographic image forming apparatuses, such as a laser printer, a laser facsimile, a digital copying machine and other known image forming apparatuses in the art. These image forming apparatuses include various types of belts, such as a photosensitive belt, a transfer belt which transfers a toner image onto a photosensitive medium, a conveying belt which conveys a printing medium, and other known belts in the art.
FIG. 1 is a schematic front view of a conventional belt driving device. As shown in FIG. 1, the conventional belt driving device is embodied as a device which drives a transfer belt used in the image forming apparatus. The conventional belt driving device includes a plurality of rollers rotatably supporting a belt 10 which performs image transferring to and conveying of a printing medium (not shown), a frame (not shown) which supports the rollers, and an elastic member 25 which applies tension to the belt 10. The rollers include a driving roller 21 which drives the belt 10 to rotate, a tension roller 23 which is elastically biased by the elastic member 25 so that the belt 10 maintains a predetermined tension, and an auxiliary roller 27 which supports the belt 10 to prevent the belt 10 from interfering with other elements.
In this conventional belt driving device, image transferring is performed at a surface of the belt 10, in a location between the driving roller 21 and the tension roller 23. To this end, each of a plurality of transfer rollers 30 is disposed at a position where a color image is transferred to the printing medium.
According to the belt driving device having the above structure, if the predetermined tension is continuously applied to the belt 10 for a long time in a state where the belt 10 is not driven, for example, when the belt driving device is manufactured and then inserted into a product, such as image forming apparatus, which is distributed or kept in a warehouse, the following problem may occur. Parts of the belt 10 which are in contact with the rollers, such as the driving roller 21 and the tension roller 23, are kept in a state where the parts are bent to have a shape of a circular arc according to the shape of the rollers. Accordingly, concentrated deformation of the belt 10 occurs at these parts. As a result, this belt deformation has an adverse effect on printing quality when an image is transferred to the printing medium.
Therefore, to avoid this problem, the tension applied to the belt 10 should be removed during a period of non-use, specifically until a user starts to use an apparatus including the belt driving device. To this end, a conventional belt driving device has been introduced as shown in FIG. 2. This belt driving device additionally includes a release spacer 50 capable of releasing the tension applied to the belt 10 during the period of non-use.
The release spacer 50 is capable of removing the belt tension during the period of non-use of the product, for example, while the product is kept in a warehouse, until the product is used for the first time. To this end, the release spacer 50 is inserted between a bushing 24 which supports the tension roller 23 and the frame 1. In this configuration, the elastic member 25 maintains a state of being pressed by the release spacer 50, so that the elastic pressure of the elastic member 25 is not transferred to the tension roller 23. Accordingly, the release spacer 50 prevents the tension from being applied to the belt 10 during a period of non-use.
According to the above structure, when the image forming apparatus is to be used for the first time, the user should remove the release spacer 50 from the belt driving device in direction A shown in FIG. 2 by hand, so that the elastic pressure of the elastic member 25 can be transferred to the tension roller 23, thus enabling the tension to be applied to the belt 10. However, a user who does not have knowledge about products using the belt 10 and the release spacer 50, such as an image forming apparatus or other known apparatuses in the art, may forget to remove the release spacer 50. Even if an installing method is described in detail in a user manual or other set of instructions, the user may install the belt 10 or product using the belt 10 without reading the manual or instructions carefully. Accordingly, the product may be used in a state where the release spacer 50 is not removed.
In this case, since the belt 10 is driven in a state where the tension is not applied to the belt 10, the belt 10 is not driven normally, thus preventing printing and other operations from being performed normally. Also, internal components of the belt driving device may be damaged, thus causing damage to the entire product.